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BeginnerPublished 2026-06-25

CCNA Default Routes: Edge-to-Core Gateway of Last Resort

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Configure a default route on a branch edge router and a return static route on an upstream core router to enable full bidirectional connectivity between a stub branch LAN and a core server LAN. Verify the S* default route, gateway of last resort, and end-to-end reachability from real hosts. Troubleshoot missing default or return paths.

Track
Est. time
40 minutes
Difficulty
Beginner
Topics

Learning objectives

  • Deploy a default static route on a branch edge router toward an upstream next-hop
  • Understand how the gateway of last resort is selected and represented as S* in the routing table
  • Configure a specific return static route on the upstream router back to the branch LAN
  • Verify routing tables and end-to-end host reachability across a routed uplink
  • Troubleshoot common default/return-path mistakes and route-to-self errors

Troubleshooting focus

  • show ip route on RTR-BR-EDGE shows no S* default: it is missing or its next-hop is wrong. Confirm the 10.0.12.0/30 link is up and the next-hop is 10.0.12.2.
  • CLIENT10's ping to 172.16.100.10 fails despite that S* default: return traffic is black-holed. RTR-CORE's route to 192.168.10.0/24 must use 10.0.12.1, not its own 10.0.12.2.
  • A host cannot reach its own gateway: CLIENT10 must use 192.168.10.1, SRV-CORE 172.16.100.1.
  • An interface is not up/up or has the wrong mask: fix that first — a static with an unreachable next-hop never installs.
  • Reachability is one-way: only the branch holds a default; RTR-CORE needs the specific route back, not another default.

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Study this topic

Free guides, a command cheat sheet, and graded practice for this lab's topic.

Learn Static & Default RoutingHow Does Routing Work? The Routing Table Explained

Grade your work

How this lab is graded
  • Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with access-class, are stated in the guide and do have to match.
  • Addresses, modes and protocol keywords are exact. An IP address, a subnet mask, switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide.
  • Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the running-config — a change that only exists in a terminal session never reaches the grader.
  • You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.
  • Scored something you believe is correct? Use Report an issue on this page — that is exactly how the grading fixes in the changelog got found.

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